Cleaning method, method for forming semiconductor structure and system thereof

ABSTRACT

A method for cleaning a reflective photomask, a method of manufacturing a semiconductor structure, and a system for forming a semiconductor structure are provided. The method for cleaning a reflective photomask includes placing a photomask in a first chamber, and performing a dry cleaning operation on the photomask in the first chamber, wherein the dry cleaning operation includes providing hydrogen radicals to the first chamber, generating hydrocarbon gases as a result of reactions of the hydrogen radicals, and removing the hydrocarbon gases from the first chamber.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims the benefit of prior filed non-provisionalapplication Ser. No. 16/943,881, filed on Jul. 30, 2020, which claimsthe benefit of prior-filed provisional application No. 62/907,963, filedon Sep. 30, 2019, under 35 U.S.C. 120.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling-down process generallyprovides benefits by increasing production efficiency and loweringassociated costs while increasing the amount of functionality that canbe provided in the reduced chip area. Such scaling down results inincreased complexities of processing and manufacturing ICs, and theprocesses required for effective quality control of the products havebecome increasingly stringent.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the embodiments of the present disclosure are best understoodfrom the following detailed description when read with the accompanyingfigures. It should be noted that, in accordance with the standardpractice in the industry, various structures are not drawn to scale. Infact, the dimensions of the various structures may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a flowchart showing various steps of a cleaning method appliedon a reflective photomask in accordance with some embodiments of thepresent disclosure.

FIG. 2 is a diagram showing a dry cleaning operation performed on aphotomask in a processing chamber in accordance with some embodiments ofthe present disclosure.

FIG. 3 is a flowchart showing various steps of a method formanufacturing a semiconductor structure in accordance with someembodiments of the present disclosure.

FIG. 4 is a diagram illustrating the method shown in FIG. 3 inaccordance with some embodiments of the present disclosure.

FIGS. 5-6 are diagrams of systems in accordance with differentembodiments of the present disclosure forming a semiconductor structure.

FIGS. 7-9 are diagrams of different tools of a system in accordance withdifferent embodiments of the present disclosure forming a semiconductorstructure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of elements and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “over,” “upper,” “on” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. Thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. The apparatus may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein may likewise be interpretedaccordingly.

As used herein, although the terms such as “first,” “second” and “third”describe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another. The termssuch as “first,” “second” and “third” when used herein do not imply asequence or order unless clearly indicated by the context.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the disclosure are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in therespective testing measurements. Also, as used herein, the terms“substantially,” “approximately” and “about” generally mean within avalue or range that can be contemplated by people having ordinary skillin the art. Alternatively, the terms “substantially,” “approximately”and “about” mean within an acceptable standard error of the mean whenconsidered by one of ordinary skill in the art. People having ordinaryskill in the art can understand that the acceptable standard error mayvary according to different technologies. Other than in theoperating/working examples, or unless otherwise expressly specified, allof the numerical ranges, amounts, values and percentages such as thosefor quantities of materials, durations of times, temperatures, operatingconditions, ratios of amounts, and the likes thereof disclosed hereinshould be understood as modified in all instances by the terms“substantially,” “approximately” or “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thepresent disclosure and attached claims are approximations that can varyas desired. At the very least, each numerical parameter should at leastbe construed in light of the number of reported significant digits andby applying ordinary rounding techniques. Ranges can be expressed hereinas from one endpoint to another endpoint or between two endpoints. Allranges disclosed herein are inclusive of the endpoints, unless specifiedotherwise.

The advanced lithography process, method, and materials described in thecurrent disclosure can be used in many applications, including fin-typefield effect transistors (FinFETs). For example, the fins may bepatterned to produce a relatively close spacing between features, forwhich the above disclosure is well suited. In addition, spacers used informing fins of FinFETs can be processed according to the abovedisclosure.

As a trend of small dimension, a photolithographic apparatus andphotolithography operations using extreme UV (EUV) radiation source andspecified photomask are introduced to the advanced generations of theelectric devices. Cleaning is one of the most important aspects ofphotomask because even the smallest contaminant may transfer defects onwafers in a patterning operation, and such contaminant can causeproximity variation to integrated circuit manufactured by suchlithography operation. To make sure the photomask meets the manufacturerequirement, the mask is scheduledly sent back to the Ebeam Operation(EBO) site (the site for manufacturing the photomask) from theFabrication (FAB) site (the site for fabricating semiconductors). Itusually takes more than 5 days at the EBO site to complete the cleaningof the photomask and send the photomask back to the FAB site.

The EUV photomask is conventionally cleaned at EBO site using a wetcleaning operation that chemicals or water can cause mask decay and maskscrap. In addition, residues and particles from the process ofde-attaching and re-attaching the pellicle of the photomask can beanother source of contaminant or defects. Therefore, the presentdisclosure provides a method for cleaning a photomask to improvecleaning efficiency and reduce possibility of further damage and/orcontamination to the photomask.

The method of the present disclosure includes performing a dry cleaningoperation on a photomask, wherein the dry cleaning operation includesproviding hydrogen radicals to a cleaning chamber to removecarbon-containing contaminant on the pellicle and the pattern of thephotomask. The method can be integrated with a manufacturing process ofa semiconductor, and thus the method can be performed at the FAB site.The method can be performed prior to or after any operation involvingthe photomask of the manufacturing process, and it takes proximal 0.2day to complete the cleaning process at the FAB site.

FIG. 1 is a flowchart of a cleaning method 100 for cleaning a photomaskin accordance with some embodiments of the present disclosure. Thecleaning method 100 includes: disposing the reflective photomask in achamber (Operation 101); providing hydrogen radicals to the chamber(Operation 102); and exposing the reflective photomask to the hydrogenradicals (Operation 103). The cleaning method 100 may further includeadditional processes according to different implementation. In someembodiments, the cleaning method 100 may further include: removingoxygen on the reflective photomask (Operation 104). In some embodiments,the cleaning method 100 may further include: removing the hydrogenradicals provided and hydrocarbon gases formed during the removal of thecarbon-containing contaminant from the chamber (Operation 105). In orderto further illustrate details of the method 100 and the concept of thepresent disclosure, illustration accompanying with a diagram as shown inFIG. 2 is provided in accordance with some embodiments of the presentdisclosure.

Referring to FIG. 2 , a photomask 201 is provided. The photomask 201includes a photomask substrate 202 and a pellicle 203. The pellicle 203is composed of a frame structure 204 and a membrane 205. The pellicle203 is to protect a pattern of the photomask substrate 202 from damageor particles from tools or environment. The membrane 205 covers thepattern of the photomask substrate 202, and the frame structure 204connects the membrane 205 to the photomask substrate 202. In someembodiments, the photomask 201 is a reflective photomask and used in anextreme ultraviolet (EUV) lithography operation. The frame structure 204includes a venting hole 206 to allow gases passing through. In someembodiments, the frame structure 204 is connected to the photomasksubstrate 202 by glue. In some embodiments, the photomask 201 includesonly the photomask substrate 202 without the pellicle 203 attached tothe photomask substrate 202 in the extreme ultraviolet (EUV) lithographyoperation.

The membrane 205 is to protect the pattern from particles from theenvironment. However, some contaminants form the environment and/or froma lithographic operation may contaminate a photomask 201 through theventing hole 206. As shown in FIG. 2 in accordance with someembodiments, contaminants may attach to the membrane 205 (e.g. thecontaminants 211), the pattern of the photomask substrate 202 (e.g. thecontaminants 212), and/or a backside of the photomask substrate 202(e.g. the contaminants 213). The contaminants 211, 212 and/or 213 canresult in defects on a semiconductor during the EUV lithographyoperation or an exposure operation of a photolithography process.

In order to remove the contaminants 211, 212 and/or 213, the photomask201 is disposed in a chamber 220 as shown in FIG. 2 to perform thecleaning operation of the method 100. Hydrogen radicals are providedinto the chamber 220 through a hole 231 on the chamber 220. In someembodiments, the hole 231 is for air or reagent injection into thechamber 220. Hydrogen radicals fill the chamber 220 and enter the spacebetween the membrane 205 and the photomask substrate 202 as shown inFIG. 2 indicated as capital H. In some embodiments, the hydrogenradicals enter the space between the membrane 205 and the photomasksubstrate 202 through the venting hole 206. Hydrogen radicals canconvert carbon and oxygen based contaminants into volatile species. Insome embodiments, the hydrogen radicals react with a carbon-containingcontaminant to form hydrocarbon gases. In some embodiments, thecarbon-containing contaminant includes at least one of carbon andhydrocarbon. The volatile species are then exhausted out through a hole232 of the chamber 220. In some embodiments, the hydrocarbon gasesformed during the removal of the carbon-containing contaminants areremoved from the chamber 220 together with unreacted hydrogen radicals.The hydrogen radicals can be a deoxidizer that to remove oxygen on thephotomask 201 to prevent oxidation of materials of the photomask 201.The oxygen is removed by a reduction reaction with the hydrogenradicals. De-oxidation of the materials of the photomask 201 by thehydrogen radicals can be another advantage of the dry cleaning operationof the method 100. Deterioration of the material of the photomask 201and damages of the pattern of the photomask substrate 202 can beprevented. Therefore, lifetime of the photomask 201 and product yieldcan be improved.

The hydrogen radicals can be generated by various methods. In someembodiments, the hydrogen radicals are generated by a plasmabombardment. In some embodiments, the hydrogen radicals are generated bya heat decomposition. It is not limited herein.

The method 100 of the present disclosure is applied on a reflectivephotomask or a photomask utilized in an EUV lithography operation. Thereflective photomask can withstand hydrogen radicals due to materialproperties of the reflective photomask, and thus the dry cleaningoperation of the method 100 can efficiently remove carbon and oxygenbased contaminants without damaging the reflective photomask. Aconventional optical photomask cannot withstand hydrogen radicals due todifferent material properties and different requirements of thephotolithography process, and the hydrogen radicals may not be appliedto the optical photomask. For instance, an attenuated phase-shift mask(APSM) is applied in technology nodes N28 or above, and an EUV mask isapplied in technology nodes N5 or below. Manufactures of differentgenerations of semiconductors involves different exposure tools withdifferent technical requirements and limitations. Conventional exposuretools and the APSM utilized in the technology nodes N28 or above are notdesigned to withstand hydrogen radicals. Materials of the pellicle 203on the conventional optical photomask can be damaged by the hydrogenradicals. However, the present disclosure is not limited herein. Withthe progress of science and technology and the change of materials, thedry cleaning operation of the present invention may be applied tovarious types of photomasks in the future.

The method 100 can be integrated with a manufacturing method of asemiconductor at one or more stages of the manufacturing method. FIG. 3is a flowchart of a method 300 for manufacturing a semiconductorstructure involving an EUV lithography operation. The method 300includes several operations as shown in FIG. 3 . The method 300includes: receiving a semiconductive substrate (Operation 301);performing a first extreme ultraviolet (EUV) lithography operation onthe semiconductive substrate by using a photomask in a first chamber(Operation 302); and performing a dry cleaning operation on thephotomask in a second chamber different from the first chamber(Operation 303).

The method 300 may further include additional operations according todifferent implementation. In some embodiments, the method 300 mayfurther include: transferring the photomask from an inspection tool tothe second chamber (Operation 304) prior to the operation 303. In someembodiments, the method 300 may further include: transferring thephotomask from the second chamber to the first chamber to perform asecond EUV lithography operation on another semiconductive substrate(Operation 305) after the operation 303. In some embodiments, the method300 may further include: transferring the photomask from an integratedreticle inspection system (IRIS) to the second chamber (Operation 306)prior to the operation 303. In some embodiments, the method 300 mayfurther include: transferring the photomask into a storage (Operation307) after operation 303. In some embodiments, the method 300 mayfurther include: transferring the photomask from a storage to the secondchamber (Operation 308) prior to operation 303 and transferring thephotomask from the second chamber to the first chamber to perform thefirst EUV lithography operation (i.e., performing operations 301 and 302after operation 303).

A photomask (such as the photomask 201 shown in FIG. 2 ) is utilized inthe EUV lithography operation performed on the semiconductive substrate.It should be noted that the operation 302 can be performed prior to orafter the operation 303. In some embodiments, the operation 303 can beperformed prior to and after the EUV lithography operation of theoperation 302. The numerals of the operations are to distinguishdifferent operations of the method 300, but it is not intended to limitthe operations to a certain sequence.

FIG. 4 shows a diagram of the aforementioned method 300 shown in FIG. 3in accordance of some embodiments of the present disclosure. Thephotomask 201 is utilized in the EUV lithography operation performed ina chamber 222. The pattern of the photomask 201 is transferred to asemiconductive substrate 241. Contaminants (e.g. the contaminants 211,212 and 213) from the environment and/or the EUV lithography operationare attached to the photomask 201. The photomask 201 is transferred tothe chamber 220 to perform the dry cleaning operation by providing thehydrogen radicals into the chamber 220. After reactions with thehydrogen radicals, volatile gases are generated from the contaminants211, 212 and 213. In some embodiments, the contaminants 211, 212 and 213from the EUV lithography operation mostly contain carbon, hydrocarbon,and/or oxygen. In some embodiments, the volatile gases include at leastone of hydrocarbon (CxHy) and dihydrogen monoxide (H₂O). In someembodiments, the operation 303 is performed after the operation 302 toremove the contaminants 211, 212 and 213 from the EUV lithographyoperation. In some embodiments, when performing operation 305, thephotomask 201 is transferred back to the chamber 222 to perform anotherEUV lithography operation on another semiconductive substrate 241 fromthe chamber 220 after the dry cleaning operation.

The pellicle 203 does not de-attached from the photomask substrate 202during the dry cleaning operation as illustrated above, and thecontaminants 211, 212 and/or 213 can be removed by the hydrogenradicals. In a conventional cleaning procedure, the photomask 201 has tobe sent to the EBO site and then sent back to the FAB site after thecleaning procedure. The conventional cleaning procedure is not just timeconsuming but also possible to damage the pattern of the photomasksubstrate 202 during the de-attaching and re-attaching process of thepellicle 203 from and to the photomask substrate 202. Therefore, thepresent disclosure provides a novel cleaning procedure which can beintegrated with the manufacturing process of a semiconductor to save thetime for cleaning the photomask 201 but also avoid damage to the patternof the photomask substrate 201 from the de-attaching and/or re-attachingprocess.

In some embodiments, the contaminants 211, 212 and 213 are from theenvironment at storage or during transportation, and the operation 303is performed prior to the operation 302 to remove the contaminants 211,212 and 213. For example, the operation 308 may be performed prior tothe operation 303. Further, the operations 301 and 302 are performedafter the operation 303. Thus, defects on the semiconductive substrate241 due to the contaminated photomask 201 during the storage can beprevented.

In some embodiments the contaminants 211, 212 and 213 being from theenvironment at the storage, the operation 303 can be performed after thephotomask 201 is transferred from the storage and prior to the operation302. In some embodiments in order to limit contamination at the storage,the operation 303 can be performed prior to the photomask 201 is sent tothe storage after the EUV lithography operation, such as the operation307. In some embodiments, the dry cleaning operation is performed aftereach of transportations of the photomask 201 between machine stations toprevent the contaminants 211, 212 and 213 moving along with thephotomask 201 to enter a next machine station.

In some embodiments, the method 300 further includes an inspectionoperation, such as the operations 304 and 306. The inspection operationcan be performed prior to and/or after the EUV lithography operation,transportation of the photomask 201, and/or storage of the photomask201. The inspection operation is performed to detect damage, defectsand/or particles on the photomask 201. Thus, a use of a damaged and/orphotomask 201 having particles attached thereon can be prevented. Itshould be noted that the particles and the contaminants referred in thespecification are different in their sizes and sources. The particlesare mostly from the EUV operation or an optical photography operation.In some embodiments, the particles are materials of (or small or tinypieces) of the photomask substrate 202 and/or of the semiconductivesubstrate 241, which may be damaged during the EUV operation or theoptical photography operation. The contaminants on the other hand aremostly from the environment. The contaminants can be elements orcompounds in the environment of the storage, the EUV or photographychamber and/or the transportation. The particles usually have a greatersize than the contaminants. In some embodiments, the contaminants have adimension less than or equal to 50 nanometers (nm), which is generallynot detectable by a photomask inspector. In some embodiments, and theparticles have a dimension greater than 100 nm. In some embodiments, theparticles may be attached to portions of the pattern of the photomasksubstrate 202 and result in defects on some portions of the patternedsemiconductive substrate 202. In some embodiments, the contaminants mayresult in a formation of a thin film (generally the thin film containscarbon) on the photomask substrate 202, and lead to an enlarged oraltered CD (critical dimensions) of patterns formed on thesemiconductive substrate 202.

However, in order to provide a better cleaning result of the photomask201, the dry cleaning operation can be performed prior to or after theinspection operation. In some embodiments, the dry cleaning operation isperformed to prevent defects on the semiconductive substrate 241 due tothe contaminated photomask 201.

FIG. 5 shows a diagram of a system 500 in accordance with someembodiments of the present disclosure forming a semiconductor structure.The system 500 is allowed to perform the method 100 and the method 300at the FAB site.

The system 500 includes a storing tool 510, an inspection tool 520, anexposure tool 530, and a cleaning tool 540. It should be noted that thesystem 500 can include other tools or machine stations for processingthe semiconductive substrate 241 or forming the semiconductor structure,as previously discussed in FIG. 2 . FIG. 5 shows only some of the toolsof the system 500 to illustrate the concept of the present disclosure,but is not intended to limit the present disclosure. The storing tool510 is for storage of the photomask 201. The inspection tool 520 is forinspecting the photomask 201 and/or performing other quality-checkingoperations before and/or after the photomask 201 is applied in the EUVlithography operation. The exposure tool 530 is to perform an exposureoperation to transfer the pattern of the photomask 201 to thesemiconductive substrate 241. In some embodiments, the exposureoperation can be an operation of the EUV lithography operation.

In some embodiments, the system 500 further includes a carrier 550,configured to transfer the photomask 201 between the storing tool 510,the inspection tool 520, the exposure tool 530, and the cleaning tool540. In some embodiments, the carrier 550 can be a robot or a machinearm. In some embodiments as shown in FIG. 5 of the system 500, thecleaning tool 540 is independent to the storing tool 510, the inspectiontool 520 and the exposure tool 530. The photomask 201 is transferred bythe carrier 550 to and from the cleaning tool 540. In other embodiments,the cleaning tool 540 can be integrated with one or more of the storingtool 510, the inspection tool 520 and the exposure tool 530.

FIG. 6 illustrates a system 600 being similar to the system 500 but thecleaning tool 540 is integrated with one or more of the storing tool510, the inspection tool 520 and the exposure tool 530 in the system600. The carrier 550 is to transfer the photomask 201 between thestoring tool 510, the inspection tool 520 and the exposure tool 530.

The cleaning tool 540 is to perform the dry cleaning operation of theoperation 303 on the photomask 201 to remove carbon-containingcontaminants attached on the photomask 201. The cleaning tool 540 in thesystem 500 or the system 600 can include a processing chamber 541(similar to the chamber 220) and a hydrogen radical producer 542. Thephotomask 201 is disposed in the processing chamber 541 during the drycleaning operation, and the hydrogen radical producer 542 is configuredto produce the hydrogen radicals into the processing chamber 541.

In order to further illustrate concepts and applications of the presentdisclosure, illustration of the method 300 applied in the system 600 inaccordance with some embodiments of the present disclosure is providedin the specification.

In some embodiments as shown in FIG. 6 and FIG. 7 , the cleaning tool540 is integrated with the inspection tool 520. Referring to FIG. 7showing the inspection tool 520 in accordance with some embodiments ofthe present disclosure, the inspection tool 520 includes an inspectionmodule 521 and a load port 522. In some embodiments, the photomask 201can be transferred between the load port 522 and the cleaning tool 540.In some embodiments, the photomask 201 can be transferred between theinspection module 521 and the cleaning tool 540. In some embodiments,the photomask 201 can be transferred to the cleaning tool 540 from or tothe inspection module 521 through the load port 522.

In some embodiments, a mask inspection is performed on the photomask 201in the inspection module 521 prior to the dry cleaning operation. Thephotomask 201 is transferred to the inspection tool 520 to perform themask inspection on the photomask 201. The method 300 can furtherinclude: determining a result of the mask inspection; and the drycleaning operation is performed if the result shows the photomask 201fails the mask inspection. If the photomask 201 fails the maskinspection, the photomask 201 is suspected also contaminated, and thecontaminants 211, 212 and 213 are suspected resulting possible defectson the semiconductive substrate 241, the dry cleaning operation isperformed after the mask inspection. The photomask 201 is transferredfrom the inspection tool 520 to the cleaning tool 540 to perform the drycleaning operation on the photomask 201.

In some embodiments, the mask inspection is performed on the photomask201 after the dry cleaning operation. The photomask 201 is transferredto the cleaning tool 540 prior to transferring to the inspection tool520. The dry cleaning operation performed prior to the mask inspectioncan remove contaminants 211, 212 and/or 213, and the mask inspection mayprovide a more accurate result of particle detection on the photomask201. The photomask 201 can be transferred back to the cleaning tool 540to perform another dry cleaning operation if the photomask 201 fails themask inspection. In some embodiments, the photomask 201 is transferredto the exposure tool 530, the storing tool 510 or another tool of thesystem 600 if the photomask 201 passes the mask inspection.

In some embodiments as shown in FIGS. 6 and 8 , the cleaning tool 540 isintegrated with the exposure tool 530. Referring to FIG. 8 showing thecleaning tool 540 integrated with the exposure tool 530 in accordancewith some embodiments of the present disclosure. The exposure tool 530includes several units. In the embodiments as shown in FIG. 8 , theexposure tool 530 includes an exposure unit 531, a load port 532, anoperator interface 533, a robot 534, and an integrated reticleinspection system (IRIS) 535. The exposure unit 531 is configured toperform the exposure operation on the semiconductive substrate 241utilizing the photomask 201. In some embodiments, the exposure unit 531includes an EUV light source. In some embodiments, the exposure unit 531includes a processing chamber similar to the chamber 222 as illustratedin FIG. 4 and previous paragraphs. The photomask 201 is loaded to orunloaded from the exposure tool 530 through the load port 532. The robot534 is configured to transfer the photomask 201 between the IRIS 535,the load port 532, the exposure unit 531 and the cleaning tool 540. Theoperator interface 533 allows an operator to control and monitortransportation and condition of the photomask 201 and the semiconductivesubstrate 241.

In some embodiments, the dry cleaning operation can be performed priorto or after the exposure operation in the exposure unit 531. The drycleaning operation performed prior to the exposure operation can reducepossibility of defects formed on the semiconductive substrate 241 due tothe contaminants on the photomask 201. The dry cleaning operationperformed after the exposure operation can remove contaminants attachedon the photomask 201 during the exposure operation before the photomask201 is used in another exposure operation or before the photomask 201 istransferred to the storing tool 510.

The IRIS 535 is configured to scan the pellicle 203 and the backside ofthe photomask substrate 202. In some embodiments, the photomask 201 istransferred to the IRIS 535 prior to the exposure operation performed inthe exposure tool 530. The method 300 can further include: transferringthe photomask 201 from the IRIS 535 to the processing chamber of theexposure unit 531. In some embodiments, similar to the mask inspection,the dry cleaning operation is performed after a scanning operationperformed in the IRIS 535. In some embodiments, the dry cleaningoperation is performed after the scanning of the IRIS 535 and prior tothe exposure operation.

In some embodiments, the dry cleaning operation is performed prior tothe scanning operation performed in the IRIS 535 and prior to theexposure operation. The photomask 201 is transferred to the cleaningtool 540 prior to transferring the photomask 201 to the IRIS 535. Insome embodiments, the dry cleaning operation is set as a routineoperation regardless the result of the scanning operation performed inthe IRIS 535. A result of the scanning operation performed in the IRIS535 is determined prior to the exposure operation. In some embodiments,if the result shows the photomask 201 is clean, the photomask 201 isthen transferred to the exposure unit 531 for performing the exposureoperation. If the result shows the photomask 201 is not clean, thephotomask 201 may be sent to clean, and the dry cleaning operation isoptionally performed again prior to the scanning operation performed inthe IRIS 535. In some embodiments, the dry cleaning operation can berepeatedly performed until the photomask 201 passes the IRIS 535.

In some embodiments, the scanning operation and the dry cleaningoperation are performed after the exposure operation. The EUV lightsource can result in decaying of materials of the photomask, and theexposure operation in the exposure unit 531 may be a source of thecontaminants. The method 300 can further include: transferring thephotomask from the processing chamber of the exposure unit 531 to theIRIS 535. The dry cleaning operation can be performed prior to or afterthe scanning operation. In some embodiments, the dry cleaning operationis performed after the scanning operation performed in the IRIS 535 andafter the exposure operation. In some embodiments, the dry cleaningoperation is performed prior to the scanning operation performed in theIRIS 535 and after the exposure operation. The dry cleaning operation isperformed to remove the contaminants from the environment during theexposure operation prior to or after the scanning operation performed inthe IRIS 535. The dry cleaning operation can be repeatedly performeddepending on different applications.

In the embodiments as shown in FIG. 8 , the cleaning tool 540 isdisposed adjacent to the IRIS 535 (or outside the IRIS 535). In someembodiments, the cleaning tool 540 is inside the IRIS 535. However, thepresent disclosure is not limited herein as long as the aboveillustrated process can be performed or the above illustrated benefitscan be achieved. In other embodiments, the cleaning tool 540 can beintegrated with one or more of the exposure unit 531, the load port 532,and the robot 534. In addition, the cleaning tool 540 can be integratedinside or outside of one or more of the exposure unit 531, the load port532, and the robot 534, and it is not limited herein.

In some embodiments as shown in FIGS. 6 and 9 , the cleaning tool 540 isintegrated with the storing tool 510. Referring to FIG. 9 shown thestoring tool 510 in accordance with some embodiments of the presentdisclosure, the storing tool 510 includes a stocker 511 and a load port512. The stocker 511 includes a space for photomask storage, and theload port 512 is to load or unload the photomask 201 into or out fromthe stocker 511. In some embodiment, the photomask 201 can betransferred between the cleaning tool 540 and the load port 512. In someembodiments, the photomask 201 can be transferred between the cleaningtool 540 and the stocker 511. In some embodiments, the photomask 201 canbe transferred between the cleaning tool 540 and the stocker 511 throughthe load port 512.

The photomask 201 is transferred to the stocker 511 of the storing tool510 for storage while the photomask 201 is not in used. The photomask201 can be transferred to the storing tool 510 from the inspection tool520, the exposure tool 530, or the cleaning tool 540. In someembodiments, the photomask 201 is transferred from the chamber 222 tothe storing tool 510 after the EUV lithography operation. In someembodiments, the photomask 201 is transferred from the inspection module521 to the storing tool 510 after the mask inspection. In someembodiments, the photomask 201 is transferred from the exposure unit 531of the exposure tool 530 to the storing tool 510 after the exposureoperation. In some embodiments, the cleaning tool 540 is integrated with(or inside) the stocker 511 as shown in FIG. 9 , but the presentdisclosure is not limited herein.

In some embodiments, the photomask 201 is transferred to the stocker 511after the dry cleaning operation. The photomask 201 can be stored at aclean condition. However, in some embodiments, the contaminants 211, 212and/or 213 may be from the environment of the stocker 511, and the drycleaning operation is performed after the photomask 201 is transferredfrom the stocker 511. The photomask 201 may be transferred out from thestocker 511 for the EUV lithography operation, the mask inspection,and/or the exposure operation. In some embodiments, the dry cleaningoperation can be a routine operation, and the photomask 201 istransferred from the stocker 511 to the cleaning tool 540 per defaulttime period. The photomask 201 is transferred from the stocker 511 tothe processing chamber 541 of the cleaning tool 540 to removecontaminants attached on the photomask 201 at the storage. Thus, thephotomask 201 is cleaned while it is used in the manufacturing processof the semiconductor structure.

The dry cleaning operation of the present disclosure uses hydrogenradicals to remove carbon and oxygen based contaminants from theenvironment, at storage, during transportation, and/or from the EUVlithography operation. The dry cleaning operation can be performedin-situ at the FAB site. Time for the in-situ dry cleaning operation canbe reduced to 0.2 days compared to the conventional wet clean at EBOsite, which takes about 5 days to send the photomask back to the FABsite. In addition, the dry cleaning operation can prevent damage anddefects resulted from the wet cleaning and/or the de-attaching andre-attaching operation in the conventional wet cleaning process.

Some embodiments of the present disclosure provide a method for cleaninga reflective photomask. The method includes: disposing the reflectivephotomask in a chamber; providing hydrogen radicals to the chamber; andexposing the reflective photomask to the hydrogen radicals.

Some embodiments of the present disclosure provide a method ofmanufacturing a semiconductor structure. The method includes receiving asemiconductive substrate; performing a first extreme ultraviolet (EUV)lithography operation on the semiconductive substrate by using aphotomask in a first chamber; and performing a dry cleaning operation onthe photomask in a second chamber different from the first chamber.

Some embodiments of the present disclosure provide a system for forminga semiconductor structure. The system includes: a storing tool,configured to store a reflective photomask; an inspection tool,configured to inspect the reflective photomask; an exposure tool,configured to perform an exposure operation to transfer a pattern of thereflective photomask to a semiconductive substrate; and a cleaning tool,configured to perform a dry cleaning operation on the reflectivephotomask to remove carbon-containing contaminant attached on thereflective photomask. The cleaning tool includes: a processing chamber;and a hydrogen radical producer, configured to produce hydrogen radicalsinto the processing chamber.

The foregoing outlines structures of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of manufacturing a semiconductorstructure, comprising: receiving a semiconductive substrate; inspectinga photomask prior to applying the photomask in an exposure operation onthe semiconductive substrate; performing the exposure operation on thesemiconductive substrate in a first chamber by using the photomask whenthe photomask passing the inspection; and performing a cleaningoperation on the photomask in a second chamber when the photomask failsto pass the inspection, wherein the cleaning operation comprises:providing hydrogen radicals to the second chamber; and removingcarbon-containing contaminants and oxygen-based contaminants on thephotomask by having the hydrogen radicals reacting with thecarbon-containing contaminants and the oxygen-based contaminants.
 2. Themethod of claim 1, wherein the photomask comprises: a substrate; and apellicle attached to the substrate, wherein the pellicle comprises aventing hole.
 3. The method of claim 2, wherein the pellicle comprises aframe structure, the venting hole is on the frame structure.
 4. Themethod of claim 3, wherein the cleaning operation comprises providingthe hydrogen radicals through the venting hole.
 5. The method of claim4, further comprising generating hydrocarbon gases as a result ofreactions of the carbon-containing contaminants and the hydrogenradicals.
 6. The method of claim 1, further comprising generating thehydrogen radicals by a plasma bombardment.
 7. The method of claim 1,further comprising generating the hydrogen radicals by a heatdecomposition.
 8. The method of claim 1, wherein the exposure operationcomprises an extreme ultraviolet (EUV) lithography operation.
 9. Amethod of manufacturing a semiconductor structure, comprising: receivinga semiconductive substrate; inspecting a photomask prior to applying thephotomask in an exposure operation on the semiconductive substrate;performing the exposure operation on the semiconductive substrate in afirst chamber by using the photomask when the photomask passing theinspection; and performing a cleaning operation on the photomask in asecond chamber when the photomask fails to pass the inspection,comprising: providing hydrogen radicals to the second chamber;generating hydrocarbon gases as a result of reactions of the hydrogenradicals to remove contaminants on the photomask; deoxidizing a materialof the photomask; and removing the hydrocarbon gases from the secondchamber.
 10. The method of claim 9, wherein the providing the hydrogenradicals comprises generating the hydrogen radicals by a plasmabombardment.
 11. The method of claim 9, wherein the providing thehydrogen radicals comprises generating the hydrogen radicals by a heatdecomposition.
 12. The method of claim 9, wherein the hydrogen radicalsenter a space between a substrate of the photomask and a pellicle of thephotomask, and the pellicle is attached to the substrate during thecleaning operation.
 13. The method of claim 9, wherein the photomaskcomprises a frame structure with a venting hole, and the hydrogenradicals is provided through the venting hole.
 14. The method of claim9, wherein deoxidizing the material of the photomask comprises removingoxygen on the photomask.
 15. The method of claim 14, wherein the oxygenis removed by a reduction reaction with the hydrogen radicals.
 16. Amethod of manufacturing a semiconductor structure, comprising: receivinga semiconductive substrate; inspecting a photomask prior to applying thephotomask in an exposure operation on the semiconductive substrate;performing the exposure operation on the semiconductive substrate in afirst chamber by using the photomask when the photomask passing theinspection; and performing a cleaning operation on the photomask in asecond chamber when the photomask fails to pass the inspection,comprising: providing hydrogen radicals to the second chamber; andgenerating hydrocarbon gases by having the hydrogen radicals reactingwith contaminants attached on the photomask, wherein the photomaskcomprises a photomask substrate and a pellicle, and the pellicle isattached on the photomask substrate during the cleaning operation. 17.The method of claim 16, wherein the second chamber has a first holeconfigured to provide the hydrogen radicals in the second chamber. 18.The method of claim 16, wherein the second chamber has a second holeconfigured to exhaust hydrocarbon gases.
 19. The method of claim 16,further comprising removing oxygen on the photomask.
 20. The method ofclaim 19, wherein the oxygen is removed by a reduction reaction with thehydrogen radicals.